1. Field of the Invention
The present invention relates to continuous variable transmissions and particularly to a self adjusting positive engagement continuous variable transmission having two differential gears arranged in sequence to deliver power to a single output shaft in continuously variable transmission ratios over a range of rotational speeds to maintain optimum acceleration.
2. Description of the Prior Art
Machines, which are powered by a rotating shaft connected to an engine, frequently require a transmission to adjust the ratio of rotational speeds between the engine and the shaft. Engines, such as gasoline engines, typically operate optimally at relatively high rates of rotational speed, in comparison to the rotational speed required for the shaft, which is powering the machine. It is conventional practice to arrange gears of varying circumference and varying numbers of gear teeth, in a power train, to reduce the output rotational speed from an optimal operating speed, for the engine, to a suitable speed, for the machine.
Certain machines must change the speed, at which they operate, during the course of operation. This is the case with motor vehicles, which must operate over a range of speeds. While the speed of a vehicle changes, during use, it is desirable to maintain the speed of the engine within a relatively narrow range, to extend the life of the engine and to maximize the power value delivered to the machine. In some cases, where an engine is being used to power a vehicle and another machine simultaneously, it may be necessary to change the speed of the vehicle but to maintain a nearly constant speed of the other machine.
Transmissions are constructed with mechanisms to deliver a selection of gear ratios to provide power at maximum torque values to a machine operating at varying speeds. Transmissions may include a sequence of gears in a power train arranged so that power is transferred from gear to gear by meshed gear teeth in positive engagement, throughout the power train. Transmission mechanisms may operate to disconnect a gear from the power train and connect another gear of different diameter and number of gear teeth, to produce a power output at a different gear ratio. Automatic transmissions may have mechanisms to stop or start one or more gears in a planetary arrangement to produce power output at differing gear ratios. Typically, clutches are employed to disengage gears to allow shifting but it is an advantage to have the entire power train in positive engagement to limit power loss due to friction and slipping. Motor vehicles may be designed with transmissions providing four or more discrete gear ratios for efficient operation over a full range of anticipated speeds of operation. Vehicles such as farm equipment, which operate within a more narrow range of speeds, may have another piece of farm equipment connected to a power out drive. The additional piece of farm equipment may require a nearly constant operational speed, thus requiring a relatively large number of gear ratios to drive the vehicle at varying speeds while maintaining the engine at a nearly constant rotational speed.
In order to provide smooth and relatively seamless gear shifting, for motor vehicles, and to provide constant rotational speed, for farm vehicles, without increasing the number of discrete gears to an impractical number, continuous variable transmissions have been developed. Continuous variable transmissions are known to be of three basic types; namely, frictional, hydrostatic, and ratcheting. U.S. Pat. No. 5,243,881, to Hayashi, discloses a control apparatus for a continuous variable transmission and describes the belt and pulley type of continuous variable transmission. U.S. Pat. No. 6,063,004, to Ibamoto, also discloses a control apparatus, for a continuous variable transmission and describes the belt and pulley type and also the frictional type of continuous variable transmission. The control apparatus receives and processes data from the engine and the machine. The control apparatus continually sends command signals to the transmission for producing the optimum transmission ratio, at any given time. These transmissions select and output continuously variable transmission ratios to a drive shaft, by applying tension or resistance, in varying degree to elements of the power train. Inevitably, some power is lost in the process of altering the transmission ratio so as to deliver power, at an appropriate torque value, to the output shaft, which drives the machine.
There is a need for a continuous variable transmission that separates power input into low gear ratio power and high gear ratio power and subsequently aggregates the power to produce a power output over a full and continuous range of gear ratios.
There is a need for a continuous variable transmission that delivers power over separate positive engagement pathways namely a low gear ratio pathway and a high gear ratio pathway for outputting power efficiently over a full and continuous range of desired gear ratios.
There is a need for a continuous variable transmission that can automatically select an optimum gear ratio without the need for a complex control mechanism. For every angular velocity on the differential gear, there is a different overall gear ratio.